Thistle Restoration -- Hull Reinforcement

I have recently begun restoration of a Thistle #411. The first step in the restoration project was removing the exterior fiberglass from the Mahogany Hull--picture--> http://www.golftoledo.net/p1000924.jpg . About half way through the removal process I discovered that the mahogany veneer and two additional layers had been sanded away in spots--probably due to dry rot. I plan on re-glassing the outside with epoxy and a thin sheet of fiberglass to preserve the wood.

My question is this: I would like to reinforce and make the hull as stiff as possible with carbon fiber. This will allow me to cover the sanded spots and also reinforce the hull. If I use 2' strips of carbon fiber what pattern should I lay out over the hull to prevent flexing of the hull. I want to preserve the look but also make her stiff as possible for racing. Oh and by-the-way, avoid the cost of using carbon fiber throughout.

 

You are taking on the same thing I did back in 1980. I had a hull #167 I think, and someone had glassed it.

The first thing you should think about if you are going to race this, is from the Thistle owners I have talked to, the wood boats are actually faster than the glass ones, so I would not cover it with anything other than epoxy resin. I stripped off the glass, sanded it down to bare wood, and replaced any wood that need to be replaced. I then repainted the hull with two part urethane. Today I wood probably not paint it. I would completely WEST it and leave the wood natural.

I completely rebuilt the centerboard trunk and keelson. I think that with new wood it is plenty stiff.

 

Thanks IKE!!!

I have noticed that if I move/push and pull the bow that there is a lot of twisting in the hull as it sits in the cradle--concerns me about stiffness. Now with that said, I realize that all of the structures that stiffen the boat need to be removed, sanded, refitted, epoxied, and reset with screws before I can judge.

I would still be interested in knowing if anyone has criss-crossed carbon fiber throughout their hull to stiffen the boat while reducing the cost of using carbon fiber throughout. Or if there is a better pattern to use for stress.

 

IKE - 2 more questions

If I decide to restore the Thistle only using a veneer of mahagony planks over the areas that have been sanded down to the second and third layers--what should i use as an adhesive for the the veneer? And should I use a router to square the existing planks out for a snug fit?

 

I would use epoxy resin. I would saturate the veneer as much as possible before I put them on. A boat this old was probably put together with a resorcinal glue such as Weldwood. I don't know if you can even get it anymore. Up until the 70's these were the best glues on the market. Their only drawback was they dried a dark red, almost purple color, and if you left any excess on the wood it really showed. Epoxy is better because it seals the wood preventing any water from getting into the wood.

 

Resorcinol is the purple stuff and is a two part, liquid, WBP structural adhesive, where as Weldwood typically is a plastic resin structural adhesive (pre-catalyzed urea formaldehyde), which is a powder that is mixed with water and cures to a brownish color. Although DAP (the Weldwood folks) also sell a resorcinol adhesive. Two different animals. Both adhesives will work and are still available, though epoxy is much easier to use, requires considerable less fuss in joint matching, is gap filling and requires much less clamping pressure to have good results.

Don't judge your Thistle too harshly Ecka00 as it's very likely she's got worn out fasteners, egged out fastener holes and is generally sloppy all over from use, repeated moisture content cycling and lack of reasonable care.

Fix her structure, reassemble and then make a decision about adding more material, to increase stiffness. Of course "stiffness" should be clearly defined for your needs, so you don't cause more harm then good, to the unstiffened areas of the structure.

Yes, using a router can clean up the edges of the veneers.

 

Dial up the Thistle web site.....Lok for Doug Laver. He is the grand Guru of Thistledom. He has spare parts and a world of experience. Pars' advice is good. Old Thistlles have often worked their fasteners loose. All those grates on the boat add a lot to the stiffness. The fasteners are famous for getting loose. and to make matters more difficult, some of the fasteners may be hiding behind bungs. Take the grates out and fix them. It's a lot of work but worth the effort.